The Banu Munajjim, was a Iranian noble-family which is known from the 9th and 10th centuries. They were descended from the Sasanian dynasty, and were closely related to the Abbasid caliphs by marriage.
According to Ibn al-Nadim, the Banu Munajjim were descended from Mihr-Gushnasp, the son of the last Sasanian king Yazdegerd III. The Banu Munajjim family is first mentioned in the 9th-century, where the eponymous ancestor of the family, Abu Mansur Munajjim (originally named Aban-Gushnasp), worked at the court of the Abbasid caliph al-Mansur as an astrologer. His son, Yahya ibn al-Munajjim, worked at the Abbasid court under al-Ma'mun, and later converted from Zoroastrianism to Islam. Yahya had four sons named Ali ibn Yahya ibn al-Munajjim, Sa'id ibn Yahya ibn al-Munajjim, Abd-Allah ibn Yahya ibn al-Munajjim, and Hasan ibn Yahya ibn al-Munajjim. These four sons would, like their father, work at the Abbasid court. Ali even befriended the caliph al-Mutawakkil, and his son Yahya ibn Ali ibn al-Munajjim did the same with al-Muwaffaq. One of Ali's other sons, Harun ibn Ali ibn al-Munajjim, also worked at the Abbasid court. Harun had a son named Ali ibn Harun ibn al-Munajjim, who later began serving the Buyids who were the new rulers of Baghdad. Ali's son Harun, is the last known member of the family.